Method for manufacturing oxygen-free copper by casting



Sept. 15, 1970 HIROSHI c w ET AL 3,528,803

METHOD FOR MANUFACTURING OXYGEN-FREE COPPER BY CASTING Filed NOV. 15,1967 GRAPH SHOW/N6 THEOXYGE/V-HWROGE/V EOU/L/BR/UM. RELATION 0F MOL TE/VCOPPER HYDROGEN 0 0.'/ ofz 0:3

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. INVENTOR S l/llFOS/V/ ICWM'A W Pal/mo MUM/5M ATTORNEYS United States3,528,803 METHOD FOR MANUFACTURING OXYGEN-FREE COPPER BY CASTING HiroshiIchikawa and Rokuro Kawanishi, Tsuchiura-shi,

Japan, assignors to Hitachi Cable, Ltd, Tokyo, Japan,

a corporation of Japan Filed Nov. 15, 1967, Ser. No. 683,285 Claimspriority, application7Japan, Dec. 28, 1966, 42/ 44 Int. Cl. C22b /14U.S. Cl. 75--76 15 Claims ABSTRACT OF THE DISCLOSURE A method ofmanufacturing oxygen-free copper, which method comprises the steps ofadding a very small amount of dehydrogenating agent to a moltenelectrolytic copper to react said dehydrogenating agent with hydrogencontained in said copper and then subjecting said dehydrogenating agentto a reaction with the oxy gen contained in the resultant molten copperand thereafter contacting dehydrogenating agent With a reducing as toeffect deoxydation of the molten copper.

BACKGROUND OF THE INVENTION The present invention pertains to theindustries for manufacturing copper articles such as wires, rod, barsand other electric articles.

It is known to subject tough-pitch copper obtained by refining copperore in a reverberatory furnace to horizontal casting to produce copperin the form, principally, of wirebar, and also cake which is small inamount. This horizontal casting system has shortcomings, for example,that the cast products have an oxygen-rich layer on their surfaces andthat the density of the castings is low.

Oxygen-free copper, in general, refers to deoxidized copper having noresidual deoxidizing agent and is characterized by not becoming brittlewhen it absorbs hydrogen, and by the superior electric conductivitywhich is at least 100%, and further by the absence of exfoliation of theoxide film.

ASTMB 170-59 describes a method for testing the increased brittleness ofcopper due to contact with hydrogen. The relationship between the oxygencontent of the copper and the increased brittleness due to theabsorption of hydrogen by the copper, the permissible oxygen content ofoxygen-free copper should be 0.0015% (15 ppm.) or less. It has beenelucidated that in case the oxygen content is in the range between0.0016% and 0.0019% (16-19 p.p.m.), the copper may or may not becomebrittle, and also that when the oxygen content is in the level of 0.02%(200 ppm), all of the test pieces invariably become brittle. While theaforesaid toughpitch copper is relatively superior in both electricconductivity and resistance to developing exfoliation of oxide film, ithas a disadvantage that it easily becomes brittle when brought intocontact with hydrogen. This poor resistance to brittleness when exposedto hydrogen is attributed to the fact that this tough-pitch coppercontains a large amount of oxygen, for example, as much as 0.032% (320p.p.m.). In spite of the recent progress in the techniques ofmanufacturing tough-pitch copper ingots in association with thetechniques of dry refining process, and despite the fact that theelectrolytic refining process has been put into practice resulting in animprovement in the purity of copper to the order of 99.997%, there-casting method has not yet undergone any drastic progress. Under suchsituation, tough-pitch copper is still used in the re-casting withoutincorporating 3,528,803 Patented Sept. 15, 1970 any improved re-castingtechniques. Thus, the purity of the cast products of copper stillremains in the range of from 99.96% to 99.97%. In order to compensatefor the shortcoming of the tough-pitch copper in becoming brittle whenit absorbs hydrogen, a proposal to deoxidize copper with phosphorous hasbeen made. This attempt, however, requires the use of a large amount ofphosphorus to reduce the oxygen content of the copper and according tothis proposed method, it has been impossible to decrease the oxygencontent to a level of 0.005% (50 ppm.) or lower. Moreover, theintroduction of a large amount of phophorus serves to markedly reducethe electric conductivity of copper which is the most outstandingproperty of the copper and at the same time results in affecting thedesirable condition of not exfoliating the oxide film. Furthermore, theuse of phosphorus gives rise to the problem in casting that suchsubstances as Cu O and P 0 are present in the interface between the moldand the ingot.

Other attempts of obtaining oxygen-free copper include the techniques ofmelting copper in vacuum. This method, however, is limited to use inlaboratories because of the equipment requirements and since the yieldis limited to the order of 500 kg. a day. Thus, this vacuum-meltingtechnique is not suitable for adoption in the production of oxygen-freecopper on an industrial basis Where quantity production is required.

Other technological problems encountered in the casting of molten copperinto oxygen-free copper ingots and cast products include the effect ofthe oxygen-hydrogen equilibrium of the molten copper on the productivityof oxygen-free copper ingots and cast products. The oxygen-hydrogenequilibrium relationship in the molten copper in general is shown in theaccompanying drawing.

The velocity of the following reaction:

(dissolved in molten copper) till an equilibrium is reached is great andthis fact has already been experienced in actual operation or in themanufacutre of tough-pitch copper in reverberatory furnaces.

In the ingots, such as wirebar, cakes and billet, which have absorbedhydrogen as the result of the aforesaid reaction, pin-hole andblow-holes which result in a reduction in the specific gravity of thecast products obtained and also the creation of unsound properties ofthe ingots produced are formed. These products present various problemswhen in use. Therefore, the greatest technological problem in themanufacture of oxygenfree copper ingots and cast products remains thecontrol of the hydrogen which is easily dissolved in molten copper.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide deoxidized copper containing no residual deoxidizing agent,namely, to provide oxygen-free copper.

Another object of the present invention is to provide oxygen-free copperwhich is superior in the property of not becoming brittle when incontact with hydrogen, which is superior in electric conductivity andwhich does not develop exfoliation of oxide film.

Still another object of the present invention is to provide a novelmethod for manufacturing oxygen-free copper, said method being such thatit is capable of extremely minimizing the oxygen and hydrogen contentsof the molten copper.

Yet another object of the present invention is to provide a novel methodfor manufacturing oxygen-free copper, which is easy and which can be putinto practice on an industrial basis and which is suitable for quantityproduction.

A further object of the present invention is to provide a novel methodfor manufacturing oxygen-free copper, said method being such that issuitable for the re-casting of copper ingots such as electrolyticcopper.

A still further object of the present invention is to provide a novelmethod for manufacturing oxygen-free copper, said method being such thatis suitable for being applied to the semi-continuous casting system andalso to the fully-continuous casting system of copper.

A yet further object of the present invention is to provide a novelmethod for manufacturing oxygen-free copper, said method being such thatcan be applied to the production of either one of the products such aswirebars, ingots, cakes, billets and moldings, irrespective of theirsize.

Another object of the present invention is to provide a novel method formanufacturing oxygen-free copper, said method being such that isextremely economical in the aspect of cost of re-casting relative to thequantity of molten metal.

Still another object of the present-invention is to provide a method formanufacturing oxygen-free copper whose oxygen content is 0.0015% ppm.)or less and whose electric conductivity is 100% or more, by the use of areducing gas.

BRIEF DESCRIPTION OF THE DRAWING Figure is an equilibrium diagramshowing the rela tions between the amounts of oxygen and hydrogenconcontained in a molten copper.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the description of thepresent invention, the terms molten copper points to such copper aselectrolytic copper or other mass of copper which requires re-castingand which is in the state of being molten by being melted in a meltingfurnace or in an electric furnace.

The term casting herein used implies the casting processes which aregenerally used in the semi-continuous casting system, as well as in thefully-continuous casting system and also in other types of castingprocess of copper. The term mold used in such casting is understood tomean such mold as is used in any one of these proc esses. The'terms castproduct of copper not only include Wirebars, ingots, cakes, billets andmold-castings, but also other cast masses obtained from casting andfurther includes all kinds of copper products obtained by furtherprocessing these cast masses into rods, wires, pipes or the like,regardless of their shape and size.

The dehydrogenating agent which is used in a very small amount in thepresent invention includes P, Li, Na, Pd and V. Besides these, Cr and Mnare also usable. The amount of such a dehydrogenating agent which isused is very small. In case the dehydrogenating agent consists of, forexample, Li, Pd or V, the amount is 0.003% or less by weight. In case itis P, the amount is in the range between 0.003% and 0.001% or less byweight. In case the dehydrogenating agent consists of other substances,the amount may be 0.0003%0.0004% by weight, or in some other cases, itmay be 0.0006 %-0.0008% by weight. With some other kind ofdehydrogenating agent, it is uniformly introduced into 16-18 tons ofmolten copper contained in a melting furnace in an amount of 0.00030.0004% by weight so that the dehydrogenating agent is uniformlycontained in the cast product in an amount 0.0003% or less by weight.These dehydrogenating agents may be introduced into the molten coppereither independently or in appropriate combination or in the form of anappropriate alloy of copper, and in appropriate shape such as ingot,plate, rod, chip, grain and powder. Such a dehydrogenating agent may becharged into the melting furnace simultaneously with the copper stockwhich is to be re-cast. Alternatively, the dehydrogenating agent may beadded to the molten copper at a desired arbitrary site or sites such asin the molten metal transport vessel, the casting holding furnace andthe casting vessel.

As some of the examples of the techniques of charging dehydrogenatingagents, grains of Cu-base alloy consisting of 15% by weight of P, and Cufor the remaining part, are introduced into the melting furnacecontinuously. Or alternatively, 0.01% by weight of P and 500 to 1000 kg.of copper billet after being deoxidized with phosphorus are chargedjointly at predetermined intervals of time. Or alternatively, coppertubes having a diameter of 15 mm. and having, therein enclosed, powderof Cubase alloy containing 15% by weight of P are charged into a meltingfurnace at predetermined intervals of time. Or alternatively, a 30 kg.of a Cu-base alloy containing 0.15% by weight of P is charged into themelting furnace at each calculated casting time.

In charging the dehydrogenating agent, it is advantageous to arrangethat the agent is contained in the copper in the stage where the latteris melted in the melting furnace, because by doing so, thedehydrogenating agent is uniformly blended in the molten copper and alsobecause the dehydrogenating agent can be made to conveniently contact areducing atmosphere, in the later stage, which is produced by the use ofa reducing agent.

The dehydrogenating functions of the aforesaid dehydrogenating agentswhich are displayed by their reaction with hydrogen, are shown, as anexample, as follows:

The significance of the use of a dehydrogenating agent in the presentinvention is described below.

FIG. 1 shows the oxygenhydrogen equilibrium of the molten copper. Anadditional explanatory statement will be hereunder made regarding thisfigure. In the case, for example, where electrolytic copper is melted ina melting furnace while being covered by a layer of charcoal and thenthe molten copper is reduced with CO in the molten copper transportvessel, the molten copper is rendered to a condition that the latterquite easily absorbs hydrogen (H and as a result, the molten copper isallowed to absorb a large amount of H till an equilibrium value isattained in accordance with the amount of the water vapor (moisture) orthe partial pressure of H in the atmosphere to which tre molten copperis exposed.

From FIG. 1 or as is clear from the reasons which will be stated later,the oxygen content of the molten copper may be arranged so as to assumean ideal value such as 0.001%0.0004% (1.0-4 p.p.m.). However, if theinside of the preserving vessel through which the molten metal is passedis kept under a reducing atmosphere by having the surface of the moltenmetal covered with a thick layer of charcoal, the molten metal will becast, with H being retained in the metal. In the fully-continuouscasting system, there is provided gas-exhausting means 1n the equipment.However, such gas-exhausting means does not evenly exhaust gas from themolten metal. If the gas-exhausting function is such that is effective,for example, up to the depth of mm. from the surface of the moltenmetal, it will remove the gas satisfactorily if the molten metal has adepth of 150 mm. or less. In the event, however, that the molten copperis as deep as 250 mm. or 400 mm., the gas expulsion function of suchmeans is not carried out with a suflicient eifectiveness, with theresult that the retention of H in the molten metal will not be avoided.If the hydrogen content of the molten meal exceeds a certain level,pinholes will develop in the ingot, and further, will result in theoccurrence of a secondary crack formation in the ingot, leading to areduction in the specific gravity of the ingot. The technologicalproblems in the present invention is focused on how to effectivelycontrol the presence of hydrogen which is easily absorbed into themolten metal during the manufacture of oxygen-free copper ingot. Inother words, the aim of the present invention lies in how to deviate theoxygen-hydrogen equilibrium from its relation diagram shown in FIG. 1and eliminate oxygen and hydrogen from the molten copper.

Various studies have been conducted to find an effective deoxidizingagent for use in molten copper. However, no systematic research has beenconducted with regard to dehydrogenating agents. As a result ofextensive experiments it has now been found that substances such as P,Li, Pd and V are effective and powerful dehydrogenating agents.

The experiments consisted of daily draining 2 tons of molten copperwhich was stabilized in an induction furnace after setting the meltingfurnace and the preserving vessel into operation, and the correspondingquantity of copper was supplemented accordingly.

When the resulting molten copper was cast in a mold, there occurred amarked rising of the surface of the metal when the copper becamesolidified. Intensive absorption of H by the copper from the moisturewhich was retained in the material which constituted the furnace wasthus confirmed. The ingot thus produced was remelted in a crude-oilfurnace, and the molten copper was transferred toanother preservationfurnace where phosphorus was introduced into the molten copper toproduce a copper ingot which had been already dioxidized 'by thephosphorus. Alternatively, the molten copper drained from thefirst-mentioned induction furnace was transferred to still anotherpreservation furnace and an ingot was produced in the same manner. Inthe case where a phosphorus containing Cu-base alloy was introduced intothe molten copper with a normal proportion of blending, no trace ofphosphorus in the cast product was detected.

Furthermore, blending of phosphorus of 3 to 5 times in amount that ofthe normal proportion was attempted. However, the cast product containedonly a trace of phosphorus. It has been found that the phosphorusintroduced first reacts with hydrogen and then with oxygen. From thisknowledge, it has been confirmed that phosphorus serves as a powerfuldehydrogenating agent. Experiments were also conducted on other agents,namely, Li, Pd and V. It was confirmed that they also had adehydrogenating function.

In the present invention, P, Li, Pd and V are used as thedehydrogenating agents for the expulsion of hydrogen from the moltencopper and also for the prevention of intrusion of hydrogen into themolten copper. The amount of the dehydrogenating agent used in thepresent invention is quite small, and in case the dehydrogenating agentconsists of P, the amount used is 0.001% or less by weight,

while in case Pd or V is used, the amount is 0.003% or less by weight.As soon as a dehydrogenating agent, for example, P, is introduced into amelting furnace which contains H the charged P begins to react with thisH (in accordance with the reaction formula already described), and thereacted P and H is discharged outside the molten copper in the form ofgas which is insoluble in the molten copper.

After there is no more H remaining in the molten copper, the P which islocated in the interface between the molten copper and the spacethereabove then reacts with the H contained in the atmosphere located inthe space above the face of the molten copper so that the P prevents theintrusion of hydrogen into the molten copper. Thus, so long as P ispresent, even in a very small amount, in the molten copper, theintrusion of hydrogen into the molten copper contained in the furnacesof the casting equipment is inhibited. As a result, the oxygen-hydrogenequilibrium in the molten copper, shown in FIG. 1, is broken. This is avery important element of the present invention. After the hydrogen hasbeen removed from molten copper, the hydrogen-free molten copper canthen be easily deoxidized by a reducing agent, for example, CO, whichwill be described later, without being restrained by the oxygen-hydrogenequilibrium of the molten copper. As a result, substantially pure coppercontaining hardly any hydrogen or oxygen can Ibe manufactured. Theamount of the dehydrogenating agent which is used in the presentinvention can be determined, within a range of a trifle amount,appropriately, in accordance with the hydrogen content of the moltencopper.

The terms reducing agent used in the present invention point to carbonmonoxide (CO), carbonic acid gas (CO carbon (C), and hydrocarbons (bothsaturated and unsaturated hydrocarbons), which may be used eitherindependently or in appropriate combination. Carbon includes charcoal.

The principal object of bringing molten copper into contact with areducing agent in the present invention resides in the expulsion ofoxygen contained in the molten copper. Therefore, the means of doing soas well as the sites where such contact is effected can vary. Ingeneral, a melting furnace is provided with an opening through which thematerials are charged. For this reason, a reducing agent such as CO isnot suitable for use in a melt ing furnace, but charcoal will satisfythe purpose. Since the molten copper transport vessels are connected toa melting furnace sideways or verticalwise in case the molten copper isdrained from the melting furnace into the trans port vessels, this meansthat the atmosphere in the melting furnace will be completelydissociated from the transport vessels and also from the subsequentstages. Both the preserving furnace and the transport vessel are, on theother hand, generally substantially closed and, therefore, they sharethe same atmosphere.

It is convenient as well as economical to cover, with charcoal, the faceof the molten copper contained in both the melting furnace and thepreserving furnace. In case where a special arrangement is provided soas to feed a reducing agent of the following composition, i.e. 70% of N28% of CO, 1% of CO and 2% of H from a protective gas generatingfurnace, the contact between the molten copper and the reducing gaswhich serves as the reducing agent can be easily and positively carriedout by feeding the gas at three sites, i.e. an upper portion of theholding furnace, a side portion and the central portion of the transportvessel and the preserving furnace, respectively. Alternatively, a thicklayer of charcoal is laid on the surface of the molten copper containedin the preserving furnace so that the gas which is produced fromimperfect combustion of the charcoal in said preserving furnace andwhich is allowed to ascend in the transport vessel may be utilized.

Where the aforesaid protective gas is used, the oxygen content of thecopper ingot and molded product can be reduced to 0.0008%0.0004% (84p.p.m.). The gas produced from imperfect combustion of charcoal iscomposed roughly of 6% of CO, 12.5% of CO and 3% of H The oxygen contentof the copper ingot and cast product obtained from the use of said gascan be reduced to 0.001% (10 ppm.) or less. As a result of variousexperiments, it has been found that, 'by the use of 4% or more by volumeof CO, the oxygen content can be decreased to 0.0006% (6 ppm). In caseCO is used, the dioxidizing action of CO will decrease where the amountof CO decreases to 4% or less. Therefore, it is desirous that additionalcharcoal be supplied to the preserving furnace to increase the amount ofCO which is generated. In case the CO is not controlled properly, theoxygen content may increase to a level of 0.0015% (15 ppm.) or more,resulting in the occurrence of brittle ingots and cast products due tothe presence of hydrogen, and therefore, attention must be paid to hecontrol of CO.

Description will hereunder be directed to the manufacture of anoxygen-free copper ingot and cast product by casting molten copper,using a fully-continuous casting equipment comprising a melting furnacehaving a charging inlet of 1300 mm. x 300 mm. in size (and made of a lowfrequency channel type induction furnace with four 3- phase inductors of1250 kva., the molten metal accommodation capacity being 16 to 18 tons,and the maximum melting capacity being 3.5 tons per hour, with thenormal melting capacity being 3.0 tons per hour), a molten metaltransport vessel (Sillit 3-phase heat generator having a capacity of 77kw.), a preserving furnace (low frequency channel type induction furnacehaving a single-phase inductor of 120 kva., with the molten metalaccommodation capacity being 2 tons), a casting vessel, a mold, and aprotective gas generator (modified propane-charcoal, the reducingcomponent being 70% of N and 30% of CO, with the capacity being 40 Nm./hr. 100 mm. water column).

Electrolytic copper plates were continuously charged into the meltingfurnace through the inlet, while copperbase alloy ingots containing0.15% by weight of phosphorus were introduced at each calculated castingtime to insure that blending be made so that the 16 to 18 tons of moltencopper in the melting furnace uniformly contained 0.0003% to 0.0004% byweight of phosphorus. A thick layer of charcoal was laid on the surfaceof molten copper contained in both the melting furnace and thepreserving furnace so as to cover the surface of the molten copper.

From the separately installed protective gas generator, a gas having thecomposition of 30% of CO and 70% of N and serving as the reducing agentwas fed to three sites, namely, a central portion of the molten coppertransport vessel, a side portion of the preserving furnace and an upperportion of the preserving furnace, through pipes, respectively.

The molten copper contained in the melting furnace was passed from theoutlet thereof into the molten copper transport vessel, and therefrom tothe preserving furnace, and therefrom into the casting vessel,successively, and then finally into the mold, and thus a desired castproduct was obtained.

In the melting furnace, among the foregoing operation steps, thedehydrogenating agent reacted with the hydrogen which was present in themolten copper as well as in the space above the face of the moltencopper, in the following manner, namely,

Kcal.

The hydrogen contained in the molten copper reacted with phosphorus andwas discharged outside the molten copper in the form of a gas insolublein the molten copper. Thus, the hydrogen contained in the molten copperwas expelled therefrom, while the hydrogen located in the space abovethe molten copper also selectively reacted with the phosphorus which waslocated in the interface between the molten copper and the space so asto prevent the hydrogen from intruding into the molten copper.

The resulting hydrogen-free molten copper was then brought into contact,in both the molten copper transport vessel and the preserving furnace,with the CO which was fed from the protective gas generator and waspositively deoxidized thereby, and thus, it was possible to obtain acast product of pure copper which hardly contains any oxygen orhydrogen.

The phosphorus content of the cast product thus obtained was 0.0005 (5'p.p.m.) or less by weight, while the oxygen content was in the rangebetween 0.0008% and 0.0004% (between 8 and 4 ppm.) by weight.

The composition of the oxygen-free copper which was produced by castingthe molten copper according to the present invention was compared withthe compositions of the already reported cast copper products, and theresult is shown in the following Table 1.

TABLE 1.OOMPARISON BETWEEN THE COMPOSITIONS OF THE COPPER OF THE PRESENTINVENTION AND THE COPPER MADE BY OTHER METHODS Oxygen-free Oxygen-Oxygen-free copper of free Toughcopper of Element the present copper ofpitch Co. 8 of invention 00. A of copper Yugoslavia U.S.A.

Percent Cu.- 99. 992-99. 996 99. 94-99. 97 99. 96-99. 99

P.p.m.:

O 4-10 320 7-10 Ag.... 9-12 10 10 9-15 Ni 1-2 (3 1 2-25 Sb 1-2 5 1 2-5As. 1-2 3 3 4-10 Fe 4-15 5 5 10-15 Sn.. 1 2 1 Tr. 1 Pb. 3-5 6 15 2-3Bi.... 1 1 1 Tr. 2 P..." 2-5 Tr. 1 Si.. l-3 3 Zn 1-8 S.. 6-10 25 2-30Se. 2 2-4 Te 1 Tr. 1

1 Not reported yet.

The cast products obtained according to the present invention are of anextremely high purity and are perfectly homogeneous in contrast to thetough-pitch copper which is heterogeneous and contains a eutectic ofCD20. For this reason, the oxygen-free copper of the present inventioncompletely eliminates the shortcomings of both the tough-pitch copperand the copper deoxidized by phosphorus of the prior art, but bears allthe strong points of these copper products of the prior art.

For example, the ingot or the cast product of the present invention issound in itself and does not tend to develop flaws during the subsequentprocessing steps. Moreover, it has a high electric conductivity, doesnot discharge any gas, can be easily processed, and can be easily drawndeeply and has a superior arc-resisting property.

Above all, the ingot and the cast product of the present invention ismanufactured in such manner that its hydrogen and oxygen contents areminimized to an extreme degree by a novel manufacturing method designedso as to break the oxygen-hydrogen equilibrium of the molten copper. Asa result, the product is given a superior property not to developexfoliation of oxide film and not to develop pinholes or blowholes inthe cast mass, and thus, the cast product of the present invention ischaracterized by its being sound in quality as a cast mass and also byhigh density of the cast mass.

The density of the cast mass of the product of the present invention iscompared with that of the toughpitch copper in the following Table 2.The superior quality of the cast product of the present invention willbe appreciated by reviewing this table.

TABLE 2 Processed Product Ingot article Oxygen-free copper of thepresent invention (gin/cm. 8. 8. 945 Tough-pitch copper (gin/emf) 8. 558. 89

Comparison of mechanical properties including resistance to bending,twisting and winding between the copper of the present invention andtough-pitch copper is shown in the following Table 3.

TABLE 3.-COMPARIS2 OF RESISTANCE TO TWISTING Since the cast product ofthe present invention has an oxygen content of 0.0015% or less as hasbeen described, it will be obviously understood that its property of notgetting brittle by contact with hydrogen is such that even when hydrogenshould intrude into the copper, the following reaction would not occur:

and thus, no brittleness from the contact with such hydrogen wouldresult. The presence of phosphorus in the cast product of copper iseffected in such pattern that the phosphorus is present in the form ofsolid solution, and this phosphorus reduces the electric conductivity ofthe product. Therefore, phosphorus is used in the present invention onlyin a very minute amount and strictly as a dehydrogenating agent. Thecontent of such phosphorus in the copper is in the order of from 0.0002%to 0.0005 (2 to 5 p.p.m.). As such, the cast product of the presentinvention is of an excellent electric conductivity.

The manufacturing method of the present invention is suitable for use inthe re-casting of, for example, electrolytic copper into a cast product.In case this method is employed in the semi-continuous casting systemand fullycontinuous casting system, it will provide a good efficiency ofthe operation, and therefore, the method of the present invention issuitable for quantity production and satisfies the industrialrequirements.

Other advantages of the manufacturing method of the present inventioninclude that it can be applied not only to the manufacture of wirebars,ingots, cakes, billets, mold-castings of both large and small size andingots of other desired shapes, but also to the manufacture of goodssuch as rods, pipes and wires which are obtained by processing theingots thus obtained continuously after the ingots are produced.

One advantage of the manufacturing method of the present invention inthe aspect of operation is that the performance and control of thismethod can be quite easily effected.

According to the present invention, where electrolytic copper isre-casted, for example, there are detected not only the elements whichconstitute the electrolytic copper, i.e. 99.997% by weight of Cu, 6.1gr./ton of Ag, 0.068 gr./ton of Au, 0.0001% by weight of Ni, 0.0001% byweight each of Sb, As, Fe and Zn and further 0.0006% by weight of S and0.0003% by weight of Pb, but also P, Li, Na or Pd which is used as adehydrogenating agent. It is, therefore, easily inferred when thesesubstances are detected by the analysis of the product, that themanufacturing method of the present invention is employed in themanufacture of such product.

What we claim is:

1. A method of manufacturing oxygen-free copper comprising:

adding an effective amount up to about 0.003% by weight of adehydrogenating agent to molten copper to react with the hydrogen insaid molten copper and thereby remove substantially all of the hydrogencontained in said copper;

contacting the dehydrogenated molten copper with a reducing agent todeoxidize the molten copper.

2. A method as defined in claim 1, wherein the eifective amount is fromabout 0.0003% to 0.003% by weight.

3. A method as defined in claim 1, wherein the dehydrogenating agent isselected from the group consisting of P, Li, Pd, Na, Cr, Mn and V.

4. A method as defined in claim 1, further comprising casting saidmolten copper into a mold to form an ingot.

5. A method of manufacturing cast oxygen-free copper ingots comprisingthe steps of:

adding an effective amount up to about 0.003% by weight of adehydrogenating agent to molten copper to cause a reaction between thedehydrogenating agent and hydrogen contained in said molten copperthereby effecting the removal of said hydrogen;

contacting said dehydrogenated molten copper with a reducing agent todeoxidize the molten copper; casting said molten copper into a mold toform ingots. 6. A method as defined in claim 5, wherein the effectiveamount is from about 0.0003 to 0.003% by weight.

7. A method as defined in claim 5, wherein the dehydrogenating agent isselected from the group consisting of P, Li, Pd, Na, Cr, Mn, and V.

8. A method of manufacturing cast oxygen-free copper ingots comprising:

admixing molten copper with an effective amount up to about 0.003% byweight of a dehydrogenating agent so as to cause reactions between thedehydrogenating agent and hydrogen contained in the molten copper andbetween the dehydrogenating agent at the top surface of the said moltencopper and the hydrogen present in the atmosphere in the space above thesurface while the copper is still in the molten state, thereby effectingdehydrogenation of the molten cop P contacting said dehydrogenaetdmolten copper with a reducing agent to deoxidize: the molten copper;

casting said molten copper into a mold to form ingots.

9. A method as defined in claim 8, wherein the effective amount is fromabout 0.0003 to 0.003% by weight.

10. A method as defined in claim 8, wherein the dehydrogenating agent isselected from the group consisting of P, Li, Pd, Na, Cr, Mn and V.

I11. A method of manufacturing cast oxygen-free copper ingots comprisingthe steps of:

adding an effective amount of up to about 0.003%

by weight of phosphorus to molten copper to cause a reaction between thephosphorus and the hydrogen contained in said molten copper therebyeffecting the removal of said contained hydrogen;

contacting said dehydrogenated molten copper with a reducing agent todeoxidize the molten copper; casting said molten copper into a mold toform ingots.

12. A method as defined in claim 11, wherein the effective amount isfrom about 0.0003 to 0.003% by weight.

13. A method of manufacturing cast oxygen-free copper ingots as claimedin claim 5, wherein the reducing agent is a reducing gas such as carbonmonoxide (CO).

14. A method of manufacturing cast oxygen-free copper ingots as claimedin claim 8, wherein the dehydrogenating agent consists of 0.0003 to0.003% by weight of phosphorus and the reducing agent is a reducing gassuch as carbon monoxide (CO) or carbon dioxide (CO 15. A method ofmanufacturing oxygen-free copper which comprises:

adding 0.0003 to 0.003% by weight of phosphorus to molten copper,wherein said phosphorus reacts with the hydrogen contained in saidmolten copper thereby removing substantially all of the hydrogen fromsaid pp contacting the dehydrogenated molten copper with a reducingagent selected from the group consisting of carbon monoxide and carbondioxide, to deoxidize the molten copper.

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